Over the past several decades the use of spark-ignited two-cycle (two-stroke) internal combustion engines has steadily increased. They are presently found in power lawn mowers and other power-operated garden equipment, power chain saws, pumps, electrical generators, marine outboard engines, snowmobiles, motorcycles and the like.
The increasing use of two-cycle engines coupled with increasing severity of the conditions in which they have operated has led to an increasing demand for oils to adequately lubricate such engines. Among the problems associated with lubrication of two-cycle engines are piston ring sticking, rusting, lubrication failure of connecting rod and main bearings and the general formation on the engine's interior surfaces of carbon and varnish deposits. The formation of varnish is a problem since the build-up of varnish on piston and cylinder walls is believed to ultimately result in ring sticking which leads to failure of the sealing function of piston rings. Such seal failure causes loss of cylinder compression which is particularly damaging in two-cycle engines because they depend on suction to draw the fuel charge into the engine cylinder Thus, ring sticking can lead to loss of power and deterioration in engine performance and unnecessary consumption of fuel and/or lubricant. Spark plug fouling and engine port plugging problems also occur in two-cycle engines.
The unique problems and techniques associated with the lubrication of two-cycle engines has led to the recognition by those skilled in the art of two-cycle engine lubricants as a distinct lubricant type. See, for example, U.S. Pat. Nos. 3,085,975; 3,004,837; and 3,753,905.
Aminophenols are useful in two-cycle engines. U.S. Pat. Nos. 4,320,020 and 4,,320,021 issued to Lange, relate to aminophenols and their use in lubricants. Aminophenols have been used in combination with dispersants and detergents. U.S. Pat. Nos. 4,100,082 and 4,200,545, both issued to Clason et al, relate to aminophenols used in combination with neutral or basic metal salts and amine dispersants in two-cycle lubricants. U.S. Pat. No. 4,379,065 issued to Lange relates to aminophenols used in combination with ashless ester dispersants. U.S. Pat. No. 4,425,138 relates to aminophenols used in lubricant-fuel mixtures for two-cycle engines.
U.S. Pat. Nos. 4,663,063 and 4,724,092 issued to Davis relate to a combination of an alkyl phenol and an amino compound in two-cycle engines. The former relates to an alkyl phenol together with an amino compound other than an aminophenol. The latter relates to an alkyl phenol together with an aminophenol.